The purpose of this study is to compare the effects of 52 weeks administration of cp-336, 156 ( an estrogen agonist/antagonist) at 4 dose level, versus placebo on bone mineral density of the lumbar spine, hip, whole body, uterine endometrium, safety and toleration. Thyroid tests are done at this site only because they are investigator-initiated in order to obtain data in thyroid binding globulin levels. The main study is conducted elsewhere. Visits to GCRC ambulatory center for thyroid testing only. This site is over subscribed.